>perl -wMstrict -le
"my $s = 'aa b: CCC DD. eee, ff ggg?';
 my $word = qr{ [[:alpha:]]+ }xms;
 my @words = $s =~ m{ $word }xmsg;
 my $result = join q{}, @words[2,3];
 print qq{'$result'};
"
'CCCDD'